Reducing contrast medium volume and tube voltage in CT angiography of the pulmonary artery

Abstract

Aim: To evaluate image quality after contrast medium (CM) and tube voltage reduction in computed tomography angiography (CTA) of the pulmonary artery.

Materials and methods: Thirty-three patients referred for CTA of the pulmonary artery for suspected pulmonary embolism were included. Patients were randomly assigned to Protocol I (100 ml of 350 mg iodine/ml iodinated CM; n=16) or Protocol II (50 ml of 350 mg iodine/ml iodinated CM; n=17). Dual-energy CT (80 kV and 140 kV) was performed in all patients. An averaged weighted series equivalent to a 120 kV image acquisition was reconstructed. The mean attenuation value of CM was measured at eight positions in the pulmonary trunk and pulmonary arteries. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Qualitative assessment of the vascular enhancement was performed independently by two experienced radiologists using a three-point scale. Mean attenuation values, image noise, CNR, and SNR of images with 50 ml CM and images with 100 ml CM were compared and mean attenuation values, image noise, CNR, and SNR in 80 kV images and 120 kV images were compared. For qualitative analysis, interobserver variability was analysed using Cohen's kappa statistics.

Results: The mean attenuation values in Protocol I and Protocol II were not significantly different at 80 kV (634.6±168.3 versus 537.9±146.7 HU; p=0.088) and 120 kV (482.8±127.7 versus 410.4±106.0 HU; p=0.085). The mean attenuation value at 80 kV was significantly higher than the mean attenuation value at 120 kV in Protocols I and II (p<0.001). The CNR and SNR were higher at 120 kV than at 80 kV in both protocols (p=0.000-0.019); however, there were no significant differences in the CNR and SNR between both protocols (p=0.600-0.952). Qualitative (subjective) analysis showed no statistical significant difference between Protocols I and II (p=0.524-1.000).

Conclusion: Low tube voltage (80 kV) CTA using 50 ml CM is not inferior to CTA at 120 kV using 100 ml CM.